(a) Related Field
The present disclosure relates to a liquid crystal display device.
(b) Description of the Related Art
A liquid crystal display device is a flat panel display device that is currently used widely and generally including two display panels on which electrodes are formed and a liquid crystal layer interposed between the two display panels. By applying a voltage to the electrodes to rearrange the liquid crystal molecules of the liquid crystal layer, the liquid crystal display device adjusts the amount of light transmitted by the liquid crystal layer to display an image.
A liquid crystal display device may have a structure in which electric field generating electrodes are provided on the two display panels. Particularly, a liquid crystal display device may have a structure in which a plurality of thin film transistors and pixel electrodes are arranged in a matrix form on a lower display panel (thin film transistor display panel), color filters of a red, a green and a blue color are formed on an upper display panel (common electrode display panel), and a common electrode covers an entire surface of the upper display panel.
However, in this liquid crystal display device, since the pixel electrodes and the color filters are formed on different substrates, it is difficult to accurately align the pixel electrodes and the color filters with each other, such that an alignment error may occur. To solve this problem, a structure (color filter on array (COA)) in which the color filters and the pixel electrodes are formed on the same substrate has been suggested.
In addition, because the upper display panel and the lower display panel are to be bonded to each other, a bonding margin is considered, and thus, a light blocking member, such as a black matrix, is usually manufactured at a size larger than a predetermined size. However, in this case, since an aperture ratio is decreased due to the increased size of the black matrix, the black matrix may be formed on the lower display panel.
A gap of the liquid crystal layer between the above-mentioned two display panels is called a cell gap and influences the general operation characteristics of the liquid crystal display device, such as its response speed, contrast ratio, viewing angle, luminance uniformity, and the like. When the cell gap is not constant, an image is not uniformly displayed over the entire screen, which causes deteriorated image quality. Therefore, to form and maintain a uniform cell gap over the entire region of the display panel, a plurality of spacers are formed on at least one of the two display panels.
The plurality of spacers may include a main-column spacer substantially supporting the two display panels and a sub-column spacer assisting in the role of the main-column space.
To simplify the manufacturing process, the light blocking member, such as the black matrix, and the spacers may be simultaneously formed by implementing a multi-step. To implement the multi-step, a mask capable of implementing a multi-transmittance and a material capable of implementing the multi-step are used. However, currently, there is a limitation in implementing the multi-transmittance in the mask, and the material capable of implementing the multi-step has not been developed until now.
Generally, a step difference between the main-column spacer and the sub-column spacer implemented using a current material is about 0.5 μm, and a density ratio of the column spaces should be accurately implemented so as to have a process margin for an active unfilled area (AUA) defect during a period in which a liquid crystal process is performed.
However, in the case in which a step protruding by a height corresponding to the column spacer is present in a region other than the main-column spacer and the sub-column spacer, the step serves as the sub-column spacer, such that entire density of the main-column spacer and the sub-column spacer is changed. This may cause a problem in a liquid crystal margin at a low temperature.
Therefore, it is important to sufficiently secure the cell gap in portions other than the spacers.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.